Check `MPSGraph.padTensor(_:with:leftPadding:rightPadding:constantValue:name)` behavior.

check.swift

#!/usr/bin/env xcrun swift

import Foundation
import MetalPerformanceShaders
import MetalPerformanceShadersGraph

let device = MTLCreateSystemDefaultDevice()!

//let size = 256 * 256 - 1 // This size should work
let size = 256 * 256 // This size may not work

let shape = [1, 1, 1, 1, size] as [NSNumber]

let graph = MPSGraph()
let input = graph.placeholder(shape: shape, name: "input")
let output = graph.padTensor(
    input,
    with: .clampToEdge,
    leftPadding: [0, 0, 2, 0, 0] as [NSNumber],
    rightPadding: [0, 0, 0, 0, 0] as [NSNumber],
    constantValue: 0.0,
    name: nil
)

let inputArrayDescription = MPSNDArrayDescriptor(
    dataType: .float32,
    shape: shape
)
let inputArray = MPSNDArray(device: device, descriptor: inputArrayDescription)

var inputValues = [Float](repeating: 0.0, count: Int(size))
for x in 0..<size {
    inputValues[x] = Float.random(in: 0.0..<1.0)
}
inputArray.writeBytes(&inputValues, strideBytes: nil)

let results = graph.run(
    feeds: [
        input: MPSGraphTensorData(inputArray)
    ],
    targetTensors: [
        output
    ],
    targetOperations: []
)

let outputData = results[output]!

var outputValues = [Float](repeating: 0, count: Int(size * 3))
outputData.mpsndarray().readBytes(&outputValues, strideBytes: nil)

print("checking...")

for d in 0..<3 {
    for x in 0..<size {
        let inputIndex = x
        let input = inputValues[inputIndex]
        let outputIndex = d * size + x
        let output = outputValues[outputIndex]
        if input != output {
            print("\(inputIndex) -> \(outputIndex): \(input) != \(output)")
        }
    }
}

print("done")